What is the Difference Between Action Spectrum and Absorption Spectrum?

The main difference between an action spectrum and an absorption spectrum lies in what they represent in the context of photosynthesis. Here are the key differences:

• Absorption Spectrum: This shows the wavelengths of light absorbed by each pigment, such as chlorophyll, in a plant. It is a graphical representation of the different wavelengths of light absorbed by different pigments and indicates the relationship between the quality of light and the absorbing capacity of pigments. The absorption of wavelengths of different pigments can be measured with a spectrophotometer.
• Action Spectrum: This shows the overall rate of photosynthesis at each wavelength of light. It is a graphical representation of the effectiveness of different wavelengths of light in photosynthesis and infers the relationship between photosynthetic activity in relation to different wavelengths of light. The action spectrum is studied in relation to oxygen evolved or carbon dioxide absorbed.

In summary, the absorption spectrum deals with the wavelengths of light absorbed by each pigment, while the action spectrum indicates the overall rate of photosynthesis at each wavelength of light and the effectiveness of different wavelengths in the process.

Comparative Table: Action Spectrum vs Absorption Spectrum

Here is a table summarizing the differences between the absorption spectrum and the action spectrum:

Both spectra display two main peaks: a larger peak at the blue region (~450 nm) and a smaller peak at the red region (~650 nm). They also have a trough in the green/yellow portion of the visible spectra (~550 nm). The action spectrum peak of chlorophyll is almost the same as that of the absorption spectrum, indicating that chlorophyll is the primary pigment in photosynthesis.